Method for electrically insulating and electronic device and device obtained thereby

ABSTRACT

A method electrically insulates an electronic device including a housing having a first face provided with a first opening closed by a PCB and a second face provided with a second opening extending facing at least a portion of at least one connection interface in which at least one first connector is connected. The method includes the steps of forming a mold around the connection interface, and while the device is placed in a vacuum enclosure, pouring a liquid resin into the mold in order to form a layer of electrically insulating material between the connector and the connection interface. A device is obtained by performing the method.

BACKGROUND OF THE INVENTION

The present invention relates to the field of electrical connection,more particularly in the field of aviation.

Connection devices are known that comprise a housing having a peripheralframe with an edge defining a first opening that is closed by a printedcircuit board (PCB) and an opposite edge having fitted thereto a platewith a second opening facing at least one electrical connectioninterface of the PCB. A well is secured on said plate so as to extendfrom an edge of the second opening to the PCB in order to receive one ormore first connectors connected to the connection interface. Theconnection interface is generally constituted by plated-through holes(PTHs) formed in the PCB and connected to conductive tracks of said PCB.The first connector comprises a rigid body having one end provided with“press-fit” type pins for engaging in the PTHs and an opposite endarranged to cooperate with a corresponding second connector. The firstconnector is connected to the second connector by pins received by forcein the PTHs.

By way of example, such connection devices are used in airplanes forconnecting the computers of the airplane to the avionics harness incompliance with the ARINC 600 standard. These computers are groupedtogether in a chassis (or a bay or a rack-mount housing) having both anopening for installing computers, and also a backplane opposite theopening, which backplane carries the connection device in such a mannerthat a computer is connected to the connection device automatically bythe computer being installed in the bay, the contacts of the computerbeing received in the connection device when the computer is in positionin the chassis. These connection devices are commonly referred to as thebackplane blocks of the rack-mount housing.

Data transfer needs have increased greatly in airplanes, such that it isnecessary to increase the density of electrical contacts. However, thisincreases problems of interference and disturbance between the contacts.

OBJECT OF THE INVENTION

A particular object of the invention is to provide connection means thatobviate the above-mentioned drawbacks, at least in part.

SUMMARY OF THE INVENTION

To this end, according invention, there is provided an electronic devicecomprising a housing having a first face provided with a first openingthat is closed by a PCB and a second face that is provided with a secondopening facing at least a portion of at least one connection interfaceextending over a first area of the PCB, with at least one well extendingfrom an edge of the second opening to the PCB so as to receive a firstconnector having a spaced-apart first surface from which there extendconductors connected to the connection interface, the device beingcharacterized in that the housing comprises a wall having a free edge ofclosed outline that bears against the PCB and that extends around theconnection interface, and in that a layer of electrically insulatingmaterial extends between the first surface of the first connector andthe connection interface to the free end of said wall, the conductors ofthe first connector passing through the layer of electrically insulatingmaterial.

The layer of electrically insulating material provides additionalinsulation. Also, the wall of closed outline thus constitutes a lostmold that serves to contain the layer of electrically insulatingmaterial while it is being put into place.

The invention also provides a method of electrically insulating anelectronic device comprising a housing having a first face provided witha first opening closed by a PCB and a second face provided with a secondopening extending facing at least a portion of at least one connectioninterface in which at least one first connector is connected, the methodcomprising the steps of:

-   -   forming a mold around the connection interface; and    -   while the device is placed in a vacuum enclosure, pouring a        liquid resin into the mold in order to form a layer of        electrically insulating material between the connector and the        connection interface.

Other characteristics and advantages of the invention appear on readingthe following description of a particular and nonlimiting implementationof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is made to the accompanying drawings, in which:

FIG. 1 is a perspective view of a connection device of the invention;

FIG. 2 is a diagrammatic view of the connection device in cross sectionon plane II of FIG. 1 ;

FIG. 3 is a fragmentary diagrammatic view in cross section on a planeperpendicular to the PCBs, showing two connectors connected together;

FIG. 4 is a front view of the first connector;

FIG. 5 is a diagrammatic view, in section on line V-V FIG. 4 , showingthe first connector; and

FIG. 6 is a fragmentary diagrammatic view in section on line VI-VI ofFIG. 3 , showing two connectors connected together.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the figures, the connection device of the inventioncomprises a housing given overall reference 1 and a printed circuitboard (PCB) 10.

The housing 1 is of rectangular box shape and it is defined by a sidewall 2 of the closed outline with one free edge forming a first face 3.1of the housing 1 and an opposite edge that is secured to a back wallforming a second face 3.2 of the housing 1. The side wall 2 forms aframe and it extends perpendicularly to the PCB 10. The first face 3.1is provided with a first opening 4.1 (defined by the free edge of theside wall 2), and the second face 3.2 is provided with second openings4.2.

The housing 1 includes wells 5, each extending from an edge of arespective one of the second openings 4.2 and each having a free edgethat is set back a little from the plane of the first face 3.1.

The second face 3.2 is provided in conventional manner with a keyingmember 6 so as to prevent assembly and connection errors.

The housing 1 is of monolithic structure: the side wall 2, the faces 3.1and 3.2, and the wells 5 comprise a single one-piece part. The housingis the result of machining a block of material, specifically a metalsuch as aluminum. Other manufacturing methods could be used. Thus, invariants, the housing could be the result of additive manufacturing orof molding. For the tightest manufacturing tolerances, it is possible toperform reworking, in particular for the first face 3.1 since itconstitutes a reference for positioning the housing 1 relative to thePCB 10.

The free edge of the side wall 2 is applied against one of the faces 11of the PCB 10, which PCB closes the first opening 3.1 and also possessesan opposite face 12. Said face 11 is provided with a connectioninterface 13 that is connected both to conductive tracks of the PCB 10and also to a connection interface carried by the opposite face 12, andnot shown herein.

The connection interface 13 extends facing the second opening 4.2 and itis surrounded by the free edge of the well 5. In this example, theconnection interface 13 comprises plated-through holes (PTHs) 14.

Two of the wells 5 each receive a first connector 100 comprising arespective dialectic support with a first end provided with conductors101, 102 of pin-shape that project from the dialectic support and thatare received by force in the plated-through holes 14. The wells 5 arearranged to guide and position the first connector 100 relative to thefirst connection interface 13. The conductors 101 of the first connector100 present a cross-section in the shape of a flattened letter S.Opposite from the conductors 101, the dialectic support of the firstconnector 100 has first electrically insulating plates 110 that areparallel to one another, each having one face carrying first signaltransport contacts 111 that are connected to the conductors 101, and anopposite face carrying a first shielding sheet 112 that is connected tothe conductors 102.

Each first connector 100 forms part of an electrical connection assemblythat also comprises a complementary second connector 200. Like the firstconnector 100, the second connector comprises a dielectric supportincluding second electrically insulating plates 210 that are parallel toone another, each having one face carrying second signal transportcontacts 211 and an opposite face carrying a second shielding sheet 212.

The contacts 111 and 211 are arranged in conductive tracks that extendparallel to a mutual engagement direction for connecting the connectors100 and 200 together. The contacts 111 and 211 are in the form ofstamped strips that are elastically deformable between a rest positionin which the strip is spaced apart from the conductive track, and adeformed position in which the strip is level with the conductive track.

The shielding sheets 112 and 212 also have contacts that are formed bystrips cut out in the shielding sheets 112 and 212 and that areelastically deformable between a rest position in which the strip isspaced apart from the shielding sheet 112 or 212 and a deformed positionin which the strip is level with the shielding sheet 112 or 212.

The contacts 111 and the shielding sheets 112 have positions that areinverted relative to the contacts 211 and the shielding sheets 212 insuch a manner that, when the first connector 100 is connected to thesecond connector 200, the plates 110 are interleaved between the plates210, and vice versa, the first contacts 111 are pressed against thesecond contacts 211, and the first shielding sheets 112 are pressedagainst the second shielding sheets 212. The contacts 111 and 211 arenarrow flat contacts for transporting signals, and the shielding sheets112 and 212 are wide flat contacts for constituting ground planesbetween zones of contacts. In this example, the contacts 111 and 211 andthe shielding sheets 112 and 212 are all made by stamping the same typeof metal sheet material, which enables contacts to be standardized forall types of signal. In this example, the width of the contacts 111 and211 is determined so as to double contact density compared with aconventional ARINC 600 connector having standard 22 gauge contacts.

The plates 210 of the second connector 200 have splines 220, eachextending between two contacts 211 parallel to the conductive tracks,and the plates 110 of the first connector 100 and have grooves 120extending between two contacts 111 parallel to the conductive tracks sothat each of them receives the free edge of a respective spline 220.

A layer 300 of electrically insulating material extends between thefirst surface of the first connector 100 and the connection interface asfar as the free edge of the side wall 2, the conductors 101 of the firstconnector 100 passing through the layer 300. The layer 300 has thicknessof about 0.6 millimeters (mm). The electrically insulating material is aroom temperature vulcanizing (RTV) silicone.

When the second connector 200 is connected to the first connector 100,the plates 210 then extend, like the plates 110, in the wells 5, whichprotect them and protect the connection; the contacts of each facingpair of contacts 111 and 211 are pressed against each other; theshielding sheets of each facing pair of shielding sheets 112 and 212 arepressed against each other; the free edge of each spline 120 is receivedin the facing groove 220.

As a result of the monolithic construction of the housing 1, itstolerance intervals are relatively tight (a few tenths of a millimeter),thus enabling the positioning of the conductors of the first connectors100 in the PCB to be more precise. This arrangement makes it possible toomit the body of the first connector 100, since the wall of the well 5is positioned and dimensioned in a manner that is sufficiently precisefor the housing 1 to be able to provide the mechanical strengthfunctions that are normally provided by the connector body. Mechanicalfunctions are thus shared between the housing and the connector.

The contacts of the first connector 100 and of the second connector 200that face one another provide electrical coupling and capacitivecoupling, without any significant break in the iterative impedance ofthe differential transmission line, thereby making possible a widepassband for digital buses (up to a few gigabits per second).

The arrangement of contacts in the first connector 100 and the secondconnector 200 thus makes it possible specifically to replace “Quadrax”type connectors while providing contact density that is greater and thusproviding better capacity to transfer signals.

The shielding sheets 112 and 212 prevent capacitive coupling betweenequipotentials of one plate 110 or 210 and the other.

The splines 120 and the grooves 220 cooperate like interdigitated combs(thus forming baffle-type passages), and the electrically insulatingmaterial of the plates 110 and 210 is selected in such a manner that thedielectric distances between adjacent contacts are artificiallyincreased and the dielectric strength of the plates 110 and 210 are muchgreater than the dielectric strength of air (in particular at lowpressure). By way of example, the dimensions and the material of thecombs are selected so as to allow a maximum direct current potentialdifference of 2100 volts (Vdc) between two adjacent contacts at altitude0. For a 0.5 mm spline 120 engaged to a depth of 0.2 mm in the groove220, the resulting insulation distance in air becomes 0.2 mm+0.5 mm+0.2mm=0.9 mm. Taking account of the dielectric strength conventionallyattributed to dry ambient air being equal to 3600 volts per millimeter(V/mm), the comb structure can withstand a potential difference of0.9×3600 V=3240 V. For air of saturated humidity, which does not occurin ventilated airplane bays, the dielectric strength that isconventionally assumed is 1000 V/m, and the comb structure can withstanda potential difference of 0.9×1000=900 V.

Since the dielectric distance in air between the conductors 110 is verysmall, and potentially too small to withstand aviation dielectricstresses, provision is made to add the layer 300, which is electricallyinsulating. The layer 300 is compressed between the first connector 100and the PCB. The layer 300 is made of a material that is elasticallydeformable and that presents electrical insulation performance betterthan that of air.

The layer 300 is made on the basis of a very liquid RTV resin, and it isshaped as follows:

-   -   at ambient pressure and temperature, the resin is applied to the        top of the PCB 10 by passing through an opening in the side wall        that is spaced apart from the PCB by a height that is greater        than the thickness desired for the layer 300. The quantity of        resin is defined so that the bottom of the dielectric support of        the first connector 100 is immersed in the resin so as to        guarantee continuity of electrical insulation. The thickness of        the resin is about 0.6 mm, since the spacing between the bottom        of the dielectric support and the top of the PCB is about 0.5        mm;    -   the device is placed in a depressurization chamber (target 10        mBar) in order to guarantee that the resin penetrates into all        of the gaps or holes in the PCB and in order to eliminate all of        the bubbles that might be present in the resin. This ensures        that, around the conductors 101 that are to be insulated from        ambient air, the resin is uniform.

It should be observed that the housing 1 and the PCB form a mold forreceiving the liquid resin. By way of example, the RTV resin used is asilicone resin, and in particular that sold under the reference “SnapsilTN3305” by the supplier Momentive. This silicone-based resin hasviscosity of 47 and is usable in the range −55° C. to +125° C.

Preferably, in order to make the first conductor 100, the contacts 111and the shielding sheets 112 are stamped (cut out and shaped) in asingle cutting and forming operation, thereby also forming theconductors 101 (press-fit pins) and shapes in relief for anchoring thisassembly in the dielectric support of the connector 100. Said dielectricsupport is made as two sub-portions in which the metal sheets and stripsare mounted. At the junction point between the two sub-portions, theanchoring shapes in relief of the strips come into abutment. Thereafter,the two insulating sub-portions are preferably welded together by anultrasonic welding technique that makes it possible, while performingthermoplastic welding, to ensure that heating is localized, therebyavoiding the use of an adhesive or of heating that is general, whichcould be a factor limiting the mechanical precision of the connector.The anchoring shapes in relief are of a size suitable for formingmechanical bonds that prevent any longitudinal movement of theconductors 101, in particular during press-fit operations.

Naturally, the invention is not limited to the embodiment described, butcovers any variant coming within the field of the invention as definedby the claims.

In particular, the device may be of a structure that is different fromthat described.

In a variant, it is possible to make the wells so that they formsockets, each suitable for receiving a respective plug of a Quadrax typeconnector, thereby making it possible to further improve the precisionwith which the plugs of the Quadrax type connector are positioned and toreduce the number of mechanical parts that need to be made.

Although in this example the means enabling the electrical path from onecontact to another comprise a comb structure, other means could beenvisaged.

It is possible to use high speed contacts for transporting highcurrents: higher currents are made possible by connecting them inparallel, and this is done on the PCB.

It is possible to use first connectors of modular sizes by creatinggroups of small signal contacts that are associated with one another bytheir dielectric support and that are associated with the shieldingsheet (or ground plane) mounted opposite from the small signal contacts.Each contact module (which would then resemble a plate 110 or 210carrying the contacts 111 or 211 and the shielding sheet 112 or 212) isassociated with another one, and so on, so as to create a firstconnector of desired size. The first connectors should be of constantwidth (the width of the plate 110 or 210), with variation being inheight only.

The dielectric support may be made by injection molding a thermoplasticor thermosetting resin.

The invention is applicable to all ARINC 600 computers, and it may beextended to any other type of computer connector that have the samerequirements, e.g. EN4165 connectors.

Using the housing as a lost mold is optional. Another solution would beto inject the same RTV resin locally while keeping it in the connectorzone by means of local leakproof barriers (made with a second RTV resinthat is more pasty).

The housing may be of a structure different from that described and itmay be made as a an assembly.

The connectors may be of a structure that is different from thatdescribed, and for example they may be of conventional structure.

The invention claimed is:
 1. An electronic device comprising a housing having a first face provided with a first opening that is closed by a PCB and a second face that is provided with a second opening facing at least a portion of at least one connection interface extending over a first area of the PCB, with at least one well extending from an edge of the second opening to the PCB so as to receive a first connector having a spaced-apart first surface from which there extend conductors connected to the connection interface, wherein the housing comprises a wall having a free edge of closed outline that bears against the PCB and that extends around the connection interface, and a layer of electrically insulating material extends between the first surface of the first connector and the connection interface to the free end of said wall, the conductors of the first connector passing through the layer of electrically insulating material.
 2. The device according to claim 1, wherein the electrically insulating material is an RTV silicone.
 3. The device according to claim 1, wherein the layer of electrically insulating material has thickness of about 0.6 mm.
 4. The device according to claim 1, wherein the PCB includes PTHs and the first connector includes pins arranged to be received tightly in the PTHs.
 5. The device according to claim 1, wherein the pins present a cross-section in the shape of the letter S. 